Production of 50 Copenhagen line 2331 or F1 hybrid male rats bearing isologously transplanted R3327, adenocarcinoma of the prostate. The rats are to be implanted subcutaneously at 2 to 3 months of age and provided for experimental use when the tumors are 2 to 3 cm. in diameter or when the rats are approximately 6 months of age. The plan is to expand the breeding colony of inbred Copenhagen line 2331 rats to meet this objective and to maintain a colony of inbred Fischer line 344 rats to provide females to mate with Copenhagen males to provide F1 hybrids for experimental use. R 3327 grows progressively in 100 per cent of inoculated F1 hybrids. These F1 hybrid males are more vigorous and more adaptable to experimental procedures than the inbred Copenhagen males. Copenhagen female rats are poor breeders due to a delayed fertility and poor lactation. Fischer females on the other hand usually prove to be good mothers. The over-all objective is to develop a model for therapeutic studies that might be applicable to human primary adenocarcinoma of the prostate.